1. Field of the Invention
The present invention generally relates to heat lamps. More specifically, the present invention relates to heat lamps for improving the temperature uniformity in a field heated by an array of heat lamps.
2. Related Art
Chemical vapor deposition (CVD) is a very well known process in the semiconductor industry for forming thin films of materials on substrates, such as silicon wafers. In a CVD process, gaseous molecules of the material to be deposited are supplied to wafers to form a thin film of that material on the wafers by chemical reaction. Such formed thin films may be polycrystalline, amorphous or epitaxial. Typically, CVD processes are conducted at the elevated temperatures to accelerate the chemical reaction and to produce high quality films. Some processes, such as epitaxial silicon deposition, are conducted at extremely high temperatures ( greater than 900xc2x0 C.).
To achieve the desired high temperatures, substrates can be heated using resistance heating, induction heating or radiant heating. Among these heating techniques, radiant heating is the most efficient technique and, hence, is the currently favored method for certain types of CVD. Radiant heating involves positioning infrared lamps around a reaction chamber positioned within high-temperature ovens, called reactors. Unfortunately, radiant energy has a tendency to create nonuniform temperature distributions, including xe2x80x9chot spots,xe2x80x9d due to the use of localized radiant energy sources and consequent focusing and interference effects.
During a CVD process, one or more substrates are placed on a wafer support (i.e., susceptor) inside a chamber defined within the reactor (i.e., the reaction chamber). Both the wafer and the support are heated to a desired temperature. In a typical wafer treatment step, reactant gases are passed over the heated wafer, causing chemical vapor deposition (CVD) of a thin layer of the desired material on the wafer. If the deposited layer has the same crystallographic structure as the underlying silicon wafer, it is called an epitaxial layer. This is also sometimes called a monocrystalline layer because it has only one crystal structure. Through subsequent processes, these layers are made into integrated circuits, producing from tens to thousands or even millions of integrated devices, depending on the size of the wafer and the complexity of the circuits.
Various process parameters must be carefully controlled to ensure a high quality of layers resulting from CVD. One such critical parameter is the temperature of the wafer during each treatment step of wafer processing. During CVD, for example, the wafer temperature dictates the rate of material deposition on the wafer because the deposition gases react at particular temperatures and deposit on the wafer. If the temperature varies across the surface of the wafer, uneven deposition of the film occurs and the physical properties will not be uniform over the wafer. Furthermore, in epitaxial deposition, even slight temperature nonuniformity can result in crystallographic slip.
In the semiconductor industry, it is important that the material be deposited uniformly thick with uniform properties over the wafer. For instance, in Very Large and Ultra Large Scale Integrated Circuit (VLSI and ULSI) technologies, the wafer is divided into individual chips having integrated circuits thereon. If a CVD process step produces deposited layers with nonuniformities, devices at different areas on the chips may have inconsistent operation characteristics or may fail altogether.
Similarly, non-uniformity or instability of temperature across a wafer during other thermal treatments can affect the uniformity of resulting structures. Other processes for which temperature control also can be critical include oxidation, nitridation, dopant diffusion, sputter depositions, photolithography, dry etching, plasma processes, and high temperature anneals.
One way that reactors have been redesigned to overcome the aforementioned problems is to provide a rotating wafer. Anexample of one such reactor is shown in U.S. Pat. No. 6,093,252. This reactor includes a circular rotatable susceptor having a diameter slightly larger than the wafer. The susceptor rotates the wafer about an axis normal to the center of the wafer. Rotation of the susceptor causes an averaging of the deposited material growth rates, alleviating the problem of concentration depletion of deposition materials as the reactant gas flows over the wafer. Rotation of the susceptor also helps to average the wafer surface temperature gradient, as all points experience all temperature environments equally. This results in a reduction in the temperature differences both within the susceptor and within the wafer being supported thereon.
In some arrangements, the infrared lamps within the reactor are positioned in manners that will facilitate controlling temperature gradients among various locations within the reaction chamber. For instance, in the illustrated arrangement, the infrared lamps generally are linear in design and are arranged in a pair of crossed arrays. The grid resulting from the crossed array configuration facilitates some control over the temperature uniformity of the wafer by adjusting the power that is delivered to any particular lamp or group of lamps; however, due to the high temperatures involved and the high degree of temperature homogeneity desired, it can be difficult to properly configure the lamp arrays to provide such uniformity.
In an effort to provide more uniform temperature distribution across the wafers, reflectors have been mounted behind the lamps to indirectly illuminate the wafers. The reflectors, or light dams, shield a portion of lamps in localized areas of concern to result in a more balanced temperature profile throughout the chamber. These reflectors generally are made of a base metal and often are gold-plated to increase their reflectivity. Planar reflecting surfaces, however, still tend to induce hot spots on wafers being heated. In addition, while the reflectors can improve the temperature profile, integrating the reflectors into a production facility has been very difficult from an assembly point of view and from an energy efficiency point of view. Furthermore, such constructions further complicate lamp bank design.
Accordingly, a need exists for a system for achieving uniform temperature distributions across semiconductor wafers during processing. Desirably, such a system should maintain the advantages of radiant heating while reducing the complexity of proper lamp bank design.
In accordance with one aspect of the present invention, a heat lamp is configured with multiple regions having varied relative winding densities. The multiple regions provide greater resolution over placement of infrared power output, and consequently, radiated heat. For instance, by providing two ends of a single lamp with more filament windings per unit length than an intermediate portion of the same lamp, the ends output more radiant energy and heat than the intermediate portion. Thus, the temperature within a region heated by the lamp will vary from one end of the lamp to the other (i.e., hotxe2x80x94coolerxe2x80x94hot).
In accordance with another aspect of the present invention, a heat lamp is configured with a non-linear structure. For instance, the heat lamp may have a generally U-shaped construction such that the lamp has two generally parallel legs separated by a bent portion. Of course, in some applications other non-linear configurations, such as C-shaped, S-shaped, L-shaped, J-shaped and the like can be used. The non-linear structure is especially advantageous in apparatus having multiple lamps operating over a given lamp array width. For instance, in lamp arrays featuring several lamps positioned side by side and extending across a width of the array (e.g., the length of a linear lamp defines a width of the array), a non-linear structure allows control of energy output along the width of the array, by controlling the lamp dimensions and/or energy input independently. In addition, where two lamps are disposed with end portions proximate one another and the leg portions extending in opposite directions, differing energy output can be provided across the array (i.e., the length of the array) as well as across the width of the array.
In accordance with a further aspect of the present invention, a non-linear lamp can be provided with a segmented filament. Such a construction provides the advantages of both constructions discussed above.
An aspect of the present invention also involves a cold wall semiconductor processing apparatus comprising a chamber defined by at least one wall, a structure for supporting a substrate within the chamber and at least one heat lamp disposed proximate the chamber. The at least one heat lamp comprises a first output region and a second output region with the first output region having a first level of radiant energy output and the second output region having a second level of radiant energy output. The first level being greater than the second level.
Another aspect of the present invention involves a chemical vapor deposition apparatus comprising a process chamber having an area for horizontal positioning of a substrate within a substrate treatment zone and having chamber walls for conducting a flow of gas across a surface of the substrate. A first bank of heat lamps are disposed generally above the substrate treatment zone and a second bank of heat lamps are disposed generally below the substrate treatment zone. The first bank has a length and a width with a first set of lamps each having a length that extends across the first bank width. The second bank has a length and a width with a second set of lamps each having a length that extends across the second bank width. The first bank width and the second bank width are disposed in generally parallel planes but extend in directions generally perpendicular to each other. At least one of the first bank and the second bank further comprises at least one lamp having means for adjusting lamp output across the corresponding one of the first bank width and the second bank width.
A further aspect of the present invention involves an apparatus for processing semiconductor wafers at elevated temperatures. The apparatus comprises a high temperature processing chamber defined by at least one wall, a susceptor disposed within the chamber for supporting a wafer to be processed and having a perimeter. A support plate has a surface generally aligned with an upper surface of the susceptor. The support plate defines an elongated opening that is asymmetric relative to the susceptor. In the illustrated embodiment, this asymmetry manifests as a xe2x80x9cringxe2x80x9d with a generally rectangular outer perimeter surrounding a round susceptor. A first array of heat lamps is disposed proximate the susceptor and a second array of heat lamps is disposed proximate the susceptor. The susceptor is disposed between at least a portion of the first array and the second array. At least one lamp of the first array or the second array comprises a higher energy output portion and a lower energy output portion. Both of the portions are at least partially disposed within a volume defined by the susceptor perimeter in a direction normal to the susceptor.
An additional aspect of the present invention comprises a method of configuring lamps in a semiconductor processing chamber heated by an array of a plurality of lamps disposed proximate the chamber. The plurality of lamps comprise at least one linear lamp having a length with the length defining a width of the array. The method comprises identifying nonuniformities in the temperature across a substrate, replacing at least one of the plurality of lamps forming the array with a corrective lamp that allows for differential power output across a width of the array. The corrective lamp is corrective in that it compensates for relatively lower or relatively higher temperature zones within the chamber to achieve better temperature uniformity throughout the substrate.